The present invention relates to the field of reaction propulsion devices, and in particular to two-propellant reaction propulsion devices, i.e. in particular rocket engines.
In the description below, the terms “upstream” and “downstream” are defined relative to the normal flow directions of the propellants in the propellant feed circuit of the reaction propulsion device.
Since the beginning of the space age, one of the main technical problems has been to ensure that thrusters are fed with propellants. Although the use of liquid propellants makes it possible to achieve controlled operation of a thruster, which does not apply with solid propellants, such liquid propellants normally need to be injected at high pressure into a propulsion chamber in order to overcome the pressure that exists inside it while the thruster is in operation. So long as the pressure inside the propulsion chamber is not too high, that can be done in comparatively simple manner by pressurizing the propellant tank. Nevertheless, if it is desired to increase the specific thrust of the thruster, it is necessary to increase the pressure inside the propulsion chamber above the pressures that can normally be achieved by pressurizing tanks. It is therefore common practice to use turbopumps to feed the propulsion chamber with propellants at very high pressure. Such a turbopump normally comprises at least one pump and at least one turbine coupled to the pump, with the pump being driven by expanding gas through the turbine. Various arrangements have been proposed for turbopumps. Thus, in certain arrangements, a single turbine drives two pumps, one for each propellant, directly or via gearing. In other arrangements, each propellant is driven by a separate turbopump. Typically, the expanding gas used for actuating the turbopump(s) comes from a gas generator, and in particular a gas generator that is also fed with propellants.
Nevertheless, that solution also presents certain drawbacks. In particular, since the propellants are highly reactive, it is generally necessary in each turbopump to isolate the combustion gas from at least one of the propellants. In particular when one of the propellants is a highly oxidizing liquid, such as liquid oxygen, for example, it is important to ensure that the flow of liquid oxygen is reliably separated from the combustion gas produced by the gas generator, since that gas is normally slightly reducing.
In such reaction propulsion devices, it is also common practice to use regenerative propulsion chambers having heat exchangers incorporated therein through which at least one of the liquid propellants passes for the purpose of cooling the walls of the propulsion chamber while preheating at least a portion of the propellant. Proposals have thus been made to make use, downstream from these heat exchangers, of the expansion of at least one propellant as preheated in this way to drive the feed turbopump(s).
French patent FR 2 031 047 thus discloses a reaction propulsion device comprising a main thruster with a propulsion chamber, a first feed circuit with a first turbopump comprising a turbine coupled to a pump in order to deliver a first propellant to the propulsion chamber of the main thruster, and a second feed circuit with a second turbopump likewise comprising a turbine coupled to a pump to deliver a second propellant to the propulsion chamber of the main thruster with a second propellant. The propulsion chamber of the main thruster is a regenerative propulsion chamber, including a first heat exchanger and a second heat exchanger.
In that prior art device, the first feed circuit passes, downstream from the first heat exchanger, through the turbine of the first turbopump, and the second feed circuit passes, downstream from the second heat exchanger, through the turbine of the second turbopump. Thus, each of the propellants is pumped to the propulsion chamber of the main thruster by a pump that is driven by a turbine actuated by expansion of the same propellant. There is therefore no need to guarantee complete separation between the pump and the turbine in each turbopump.
Nevertheless, in that prior art device, since all of the flow of each of the two propellants is expanded through the turbine of the corresponding turbopump prior to being injected into the propulsion chamber, the injection pressure and thus the pressure in the propulsion chamber and also the specific thrust remain limited.